D. N. Klochkov

Nonlinear excitation of zonal flows and streamers in plasmas

Nonlinear excitation of zonal flows and streamers in plasmas is considered. The emphasis is given to the nonlinear interaction of low- and high-frequency drift waves which can result in the excitation of zonal flows and streamers in a plasma of fusion devices. For this purpose, an inhomogeneous nonisothermal plasma in a strong external magnetic field whose characteristic frequencies are lower than the ion Langmuir frequency but higher than the collision frequency is studied. The excitation of a long-wavelength low-frequency drift wave during the development of the nonlinear modulational interaction of a high-frequency drift pump wave is investigated. The growth rates of the modulational instability are obtained, and the conditions for its development are determined. Self-organized structures described by solutions of evolutionary equations for the modulational interaction are associated with zonal flows and streamers. A possible relation of the modulational interaction in Earth’s ionospheric plasma to the...

Nonresonant radiative Pierce instability and its saturation—Chaos

The review of theoretical investigations of a nonresonance stimulated Pierce radiation by the relativistic electron beam (REB) in a waveguide is presented. REB is supposed to be stabilized by an infinitely strong longitudinal magnetic field. Using the analytical methods of linear theory, the conditions leading to the rise of radiative Pierce instabilities, their growth rates and the radiation spectrum are determined. By numerical modeling of the problem, the efficiency of beam energy transformation into electromagnetic field energy as a function of the beam current, its relativism, and geometry are calculated. The physical nature of the instability is clarified and its saturation mechanisms are discussed. In particular, in the saturated state the chaotic motion of beam particles and chaos in the radiation spectrum are observed.

On the instability of a two-dimensional plane plasma crystal

A study is made of the transverse instability of two-dimensional plane dust crystals with a simple (one particle per primitive cell) and a complex (two particles per primitive cell) lattice structure. The instability criteria (crystal melting conditions) are obtained for an arbitrary, spherically symmetric intergrain interaction potential. It is shown that, for simple lattices, the instability develops in the short-wavelength limit, whereas, for complex lattices, the instability growth rate is maximum in the long-wavelength limit. The structural instability of a square lattice is also considered.

On the types of instability of spatially restricted systems

A classification of instabilities in spatially restricted systems is presented, which generalizes a classification considered in book [1]. It is shown that, if a system has no active boundaries and the waves are not amplified in an infinite homogeneous medium, which corresponds to the absence of solutions of the dispersion equation with the negative imaginary part of the wave vector at the real frequency, then only nonamplified instabilities with a nonlocal resonance can be developed. The development of nonamplified instability is considered in a spatially restricted system through which a flux propagates, when along with natural waves the excitation of the waves of fluxes playing a key role in the development of the instability is taken into account.

Theory of stimulated nonresonant emission from relativistic beams

A study is made of the radiative Pierce instability of a relativistic electron beam in a waveguide stabilized by an infinitely strong magnetic field. Analytical and computational methods are used to determine the growth rate of the instability, as well as the efficiency for conversion of the beam energy into electromagnetic field energy as a function of the beam current, how relativistic the beam is, and the geometry of the system. The physical nature of the instability is clarified and the mechanisms for its saturation are discussed.

Ponderomotive force of the low-frequency field and modulational instability of drift waves

A study is made of the processes that occur in an inhomogeneous nonisothermal plasma in a strong external magnetic field and whose characteristic frequencies are lower than the ion Langmuir frequency but higher than the collision frequency. An expression for the ponderomotive force of the low-frequency field is derived. The excitation of a long-wavelength low-frequency drift wave during the development of the modulational instability of a drift pump wave is investigated. The growth rates of the instability are obtained, and the conditions for its onset are determined. The possible relation of the modulational instability to the formation of structures in the plasma is discussed.

Effect of the plasma electron motion on the development of Cherenkov instability in a waveguide

A linear theory of the Cherenkov amplification in a transversely nonuniform waveguide in an infinitely strong magnetic field is constructed with allowance for both ordered and thermal motions of plasma electrons. The effect of these electron motions on the threshold for the onset of Cherenkov instability is investigated. The amplification coefficients and the conditions for the onset of the instability are determined.

Electromagnetic theory of the radiative Pierce instability

Nonresonance microwave sources based on the stimulated Pierce radiation of relativistic electron beams in smooth waveguides are presented. The microwave Pierce oscillator is a smooth cylindrical waveguide, along the axis of which a straightline relativistic electron beam propagates. To derive the growth rate of the radiative Pierce instability, the energy change of an electron propagating through the waveguide is calculated.